Heart disease, specifically coronary artery disease, is a major cause of death, disability, and healthcare expense in the United States and other industrialized countries. A number of methods and devices for treating coronary heart disease have been developed, some of which are specifically designed to treat the complications resulting from atherosclerosis and other forms of coronary arterial narrowing.
One method for treating such conditions is percutaneous transluminal coronary angioplasty (PTCA). Generally, PTCA is a procedure that involves passing a balloon catheter over a guidewire to a stenosis with the aid of a guide catheter. The stenosis may be the result of a lesion such as a plaque or thrombus. The guidewire extends from a remote incision to the site of the stenosis, and typically across the lesion. The balloon catheter is passed over the guidewire, and ultimately positioned across the lesion. Once the balloon catheter is appropriately positioned across the lesion, e.g., under fluoroscopic guidance, the balloon is inflated to break-up the plaque of the stenosis to thereby increase the vessel cross-section. The balloon is then deflated and withdrawn over the guidewire into the guide catheter to be removed from the body of the patient. In many cases, a stent or other prosthesis must be implanted to provide permanent support for the vessel. Stents are typically constructed of a metal or polymer and are generally a hollow cylindrical shape. When such a device is to be implanted, a balloon catheter, typically carrying a stent on its balloon, is deployed to the site of the stenosis. The balloon and accompanying stent are positioned at the location of the stenosis, and the balloon is inflated to circumferentially expand and thereby implant the stent. Thereafter, the balloon is deflated and the catheter and the guidewire are withdrawn from the patient.
Although systems and techniques exist that work well in many cases, no technique is applicable to every case. For example, special methods exist for dilating lesions that occur in branched or bifurcated vessels. A bifurcation is an area of the vasculature where a main vessel is bifurcated into two or more branch vessels. It is not uncommon for stenotic lesions to form at such bifurcations. The stenotic lesions can affect only one of the vessels, i.e., either of the branch vessels or the main vessel, two of the vessels, or all three vessels.
Methods to treat bifurcated vessels seek to prevent the collapse or obstruction of the main and/or branch vessel(s) during the dilation of the vessel to be treated. Such methods include techniques for using double guidewires and sequential percutaneous transluminal coronary angioplasty (PTCA) with stenting or the “kissing balloon” and “kissing stent” techniques, which provide side branch protection. Administering PTCA and/or implanting a stent at a bifurcation in a body lumen poses further challenges for the effective treatment of stenoses in the lumen. For example, dilating a vessel at a bifurcation may cause narrowing of an adjacent branch of the vessel. In response to such a challenge, attempts to simultaneously dilate both branches of the bifurcated vessel have been pursued. These attempts include deploying more than one balloon, more than one prosthesis, a bifurcated prosthesis, or some combination of the foregoing. However, simultaneously deploying multiple and/or bifurcated balloons with or without endoluminal prostheses, hereinafter individually and collectively referred to as a bifurcated assembly, requires highly accurate placement of the assembly. Specifically, deploying a bifurcated assembly requires positioning a main body of the assembly within the trunk of the vessel adjacent the bifurcation, and then positioning the independent legs of the assembly into separately branching legs of the body lumen.
Implanting a stent at a bifurcation in a body lumen requires additional consideration of appropriate stent sizes due to the relative sizes of the main vessel and the branch vessels. Some branch vessels can have somewhat smaller diameter lumens than the main vessel from which they branch. In addition, some branch vessels can have lumens with somewhat different diameters from each other. Therefore, stents of different sizes may be needed for properly deploying a stent in each of the main and branch vessels. It would be desirable to allow a clinician to custom-select different combinations of stent sizes for deploying stents in main or branch vessels having different diameter lumens. Further, it would be desirable to allow for differential sizing of a side branch stent even after the main vessel stent is implanted.
Further, stent implantation may cause undesirable reactions such as restensosis, inflammation, infection, thrombosis, and proliferation of cell growth that occludes the passageway. These reactions are especially common when repairing a vessel affected by stenosis at the point at which the vessel originates, branching off from an adjoining vessel. This point of origin is referred to as the ostium of the vessel, which is prone to restenosis. A bulk of material (such as, for example, overlapping stent struts) often occurs at the ostium and acts as an initiation site for thrombus and/or restenosis. To assist in preventing these conditions, stents have been used with coatings to deliver drugs or other therapeutic agents at the site of the stent. However, it would be desirable to provide a side branch stent having a design or structure that allows for less turbulent blood flow at the ostium and thus minimizes undesirable reactions such as those listed above.